roads, is advantageous not only for the saving of power | but the saving of painful sensations to the traveller. The suffering usually endured in ordinary modes of land conveyance is that which chiefly arises from friction. Friction is the grand evil to be overcome. Were friction altogether removed, we should feel no sensation in moving; as, for example, we experience no sensation of motion in being carried along with the earth in its ceaseless rotations, although proceeding at an inconceivable velocity. It may be argued from these premises, that no one need fear to be carried along at any rate of speed-even a hundred miles an hour-provided the motion be perfectly smooth or free from friction, and that there is a protection from the atmosphere. Practically, in locomotion upon railways, a small degree of friction is required between the wheels and the rails, to cause adhesion, and this is accomplished by the ordinary roughness of the iron. Rails. The experience of ten years has introduced a few improvements in the construction and management of lines of railroad. At first, malleable iron rails were supposed to be preferable to those of cast-metal; but now it is understood that cast rails, if properly made, will endure all the tear and wear to which they can be fairly subjected. To be of the strongest and best form, each individual rail should be at least twelve feet in length, six inches in depth at the two ends, and thence gradually deepening beneath in the fish-belly form to the centre. The thickness should be fully one inch, and the upper surface, on which the wheel is to run, should be an inch and three-quarters or two inches, so as to project laterally like the cross top of the letter T. The rails are to be supported at their joint extremities, where they are pinned together, and also at intervals of every three feet. The supporters should consist of transverse bars of wood, sunk in the ground; by being thus crossing from the one track to the other, both lines of rail are kept from separating or shifting, and if there is any tendency to subside, both are equally lowered. On many lines of railroad stone sleepers are preferred to wood, but, as it seems, with no adequate advantage. Stone sleepers present too unyielding a base to the rolling of the wheels, and cause a jolting most injurious to the mechanism of the carriages. In several instances, lines with stone sleepers have been taken up, and wood substituted. The railways in Belgium are laid on wood. To attain the highest perfection in the mode of laying rails, a plan has been followed on the Newcastle and Shields line, and also on that of the Great Western between London and Bristol, of placing rails having an even under side upon longitudinal beams of timber, which are united at certain intervals by transverse bars: thus the whole substructure is a handsome framework laid on the ground, and presents the best species of support. In general, this will be found too expensive a kind of railway; and it may be anticipated that the method of fixing rails upon cross bars of wood, at intervals of three feet, will ultimately come into universal use. out track branches from the main one. This rail is two or three feet, more or less, in length, and one end may be moved over that angle, and laid so as to form a part of the main track, or the turn-out track. The switch rail is usually moved by the hand, so as to form a part of that track on which the waggon is to move. Carriages-Wheels.-The principal consideration, in regard to the construction of carriages, relates to their bearings on the axle and the rim of the wheel. The rule given by Mr Wood, as to the bearing on the axle, is, that in order to produce the least friction, the breadth of the bearing should be equal to the diameter of the axle at the place of bearing. This diameter must be determined by the weight to be carried; and the breadth of the bearing will accordingly vary with it. In order to keep the wheels fairly on the rails, they are furnished with thin edges which dip on the outside; these flanges are about an inch and a half in depth. The mid wheels of locomotives are now made without flanges, but the fore and hind pair require flanges of rather more than usual depth. Wheels of large diameter move with greater ease over the rails than those which are small, because the large ones, in this as in all similar cases, have more power in overcoming obstacles. Yet there is a proper medium in the dimensions of wheels. Large wheels are inconvenient in point of height, and are apt to produce a rocking motion. It would appear that the most suitable diameter for the waggon or carriage wheels is from two and a-half to three feet, which is the usual size. The wheels of the locomotive have a diameter of about four feet; to make them broader is considered injudicious. Curvatures in the Road.-The curvatures of the railroad present some obstructions, since the axles of the car and waggons being usually fixed firmly to the frames, every bend of the tracks must evidently cause some lateral rubbing, or pressure of the wheels upon the rails, which will occasion an increased friction.* If the wheels are fixed to the axles, so that both must revolve together, according to the mode of construction hitherto most usually adopted in passing a curve, the wheel that moves on the outside or longest rail must be slided over whatever distance it exceeds the length of the other rail, in case both wheels roll on rims of the same diameter. This is an obstruction presented by almost every railroad, since it is rarely practicable to make such a road straight. The smallest curvature that is allowable should not be less than a radius of 300 feet. In going round a height, the radius should on no account be so small as this, in order that the engine drivers may have a clear look-out ahead, and so prevent collisions and overtakings on the road. Inclined Planes.-Where the inclination of the road is greater than that for which the ordinary power is calculated, the ascent must be effected by means of an additional power, the amount of which can be readily computed, since in those parts no additional friction of the cars or wheels is to be provided for, and only the additional resistance arising from gravity is to be overcome. If, for instance, the additional inclination is one in ninety-six, or fifty-five feet in a mile, the additional power must be to the weight as one to ninetysix, or as fifty-five to the number of feet in a mile, namely, 5280. In descending planes, so much inclined that the gravity would move the carriages too rapidly for safety, the velocity is checked by means of a break, which consists of a piece of wood of the same curvature as the rim of a set of the wheels, upon which the break is pressed by means of a lever, so adjusted as to be within reach of the conductor, in his position on the carriage. Turn-outs. If all the waggons upon a railroad, whether for the transportation of passengers or merchandise, were to travel at the same time, and at the same speed, two sets of tracks would be sufficient to accommodate the whole, as there would be no necessity of their turning out to pass each other. But in the transportation of passengers, greater speed is desirable than in the transportation of merchandise; for the transportation of merchandise, whether by horse power or steam power, can be done more economically, and with less injury to the road, at a low than a very high rate of speed. It is, therefore, a very considerable Locomotive Engines.- Within the last few years, object, in railroads upon lines of public travel, to allow very considerable improvements have been made in the waggons to pass others travelling in the same direction. construction of the locomotives by which the draught Provision must be made, accordingly, for turning out. of the trains of carriages is effected. Originally the This provision is particularly necessary in case of a locomotive was placed upon four wheels, the two front road with a single set of tracks, on which the carriages ones being smaller than those behind. Now, six wheels must meet. These turn-outs are made by means of a are employed, the front and hind pair being smaller moveable or switch rail at the angle where the turn-than those in the middle, these middle ones being the | wheels upon which, by the action of cranks from the engine, the whole mass is propelled. As may be seen by the small annexed engraving, which represents a railway train, the locomotive consists of a long iron barrel or cylinder supported by six wheels, with a chimney rising in front, and affording standing space behind for the engineer who conducts and regulates plane rising 1 in 96, and extending 1 mile, the engine the machine. It is unnecessary to confuse the mind was assisted by another engine called the Samson, of the unscientific reader with a minute account of this and the ascent was performed in 9 minutes. At startwonderful apparatus; it will suffice to say, that the ending, the fire-place was well filled with coke, and the of the barrel-like object next the engineer, consists of coke supplied to the tender accurately weighed. On a furnace or fire-box, and the heat generated in it by arriving at Manchester, the fire-place was again filled, the consumption of coke, is conducted thence through and the coke remaining in the tender weighed. The a great number of tubes in the cylinder, and finally consumption was found to amount to 929 pounds net escapes at the chimney. The cylinder in which the weight, being at the rate of one-third of a pound per water is boiled and steam generated, is sheltered from ton per mile. Speed on the level was 18 miles an hour; the external air by a case; and by receiving the action on a fall of 4 feet in a mile, 21 miles an hour; fall of of heat from so many tubes passing through it, the 6 feet in a mile, 25 miles an hour; on the rise over steam is rapidly generated for the use of the engine. Chatmoss, 8 feet in a mile, 17 miles an hour; on level The engine lies horizontally beneath the chimney, and ground sheltered from the wind, 20 miles an hour. The in such a position as to permit the working of the piston wind was moderate, but direct ahead. The working upon the crank of the axle of the middle set of wheels. wheels slipped three times on Chatmoss, and the train By means of lever handles affecting the mechanism, the was retarded from two to three minutes. The engine, engineer can at pleasure produce or stop the motion, on this occasion, was not examined before or after the as effectually and much more readily than a coach- journey, but was presumed to be in good working order. driver could set off or arrest the progress of his horses. On the 29th of May, the engine called the Samson Immediately behind the locomotive is a carriage called (weighing 10 tons 2 cwt., with 14-inch cylinders, and the tender, which is loaded with a supply of fuel and a 16-inch stroke; wheels 4 feet 6 inches diameter, both tank round its sides containing water. The weight of pairs being worked by the engine; steam 50 lbs. presa locomotive, supplied with its proper quantity of water sure, 130 tubes) was attached to 50 waggons laden with and fuel, is about twelve tons. The tender, when filled merchandise; net weight about 150 tons; gross weight, with water and fuel, weighs seven tons: it can carry including waggons, 223 tons 6 cwt. The tender weighed 700 gallons of water, and eight hundredweight of 7 tons, making a gross load (including the engine) of coke forms a sufficient supply for a trip of from thirty 240 tons 8 cwt. The engine with this load travelled to forty miles with an ordinary load. The cost of a from Liverpool to Manchester (30 miles) in 2 hours locomotive is about £1700, and it seldom wears longer and 40 minutes, exclusive of delays upon the road for than two years without undergoing a very extensive watering, &c.; being at the rate of nearly 12 miles an repair. On the Great Western Railway, which is of hour. The speed varied according to the inclinations unusual breadth of track, the locomotives are much of the road. Upon a level, it was 12 miles an hour; larger and more powerful. Ordinary locomotives eva- upon a descent of 6 feet in a mile, it was 16 miles an porate seventy-seven cubic feet of water per hour, but hour; upon a rise of 8 feet in a mile, it was about 9 those on the Great Western evaporate about 200 cubic miles an hour. The weather was calm, the rails very feet. It is calculated that the evaporation of one cubic wet; but the wheels did not slip, even in the slowest foot per hour, produces a gross mechanical force of speed, except at starting, the rails being at that place nearly two horse power; consequently, to ascertain the soiled and greasy with the slime and dirt to which they power of a locomotive, we must multiply by two the are always exposed at the stations. The coke consumed number of cubic feet which it evaporates per hour. in this journey, exclusive of what was raised in getting In common circumstances, an ordinary sized locomo- up the steam, was 1762 lbs., being at the rate of a tive exerts a power of 150 horses, and a larger one quarter of a pound per ton per mile." exerts a power of 400 horses. To estimate this degree of force, it is necessary to recollect that a horse upon a common road cannot draw for any length of time more than fifteen hundredweight, while on a railway it will pull with equal ease ten tons, being thirteen times the amount. We may now, therefore, compute that the power of a locomotive such as is usually employed, is equal to a draught of 1500 tons. With this weight to drag, however, only a slow motion is obtainable; and to procure the necessary speed of from twenty to twentyfive miles per hour, the load must be proportionally diminished. Something must also be allowed for the difficulty of ascending inclined planes. A weight of from 100 to 150 tons is considered a fair load for a locomotive to draw; but it is seldom more than sixty to seventy tons. The following experiments on the power of draught were made by Dr Lardner on the Liverpool and Manchester Railway in 1832 : "On Saturday the 5th of May, the engine called the Victory took 20 waggons of merchandise, weighing gross 92 tons, 19 cwt. qr., together with the tender containing fuel and water, of the weight of which I have no account, from Liverpool to Manchester (30 miles), in 1 hour, 34 minutes, 45 seconds. The train stopped to take in water half-way for 10 minutes, not included in the above-mentioned time. On the inclined General Appearance and Management.-In America and Belgium, most lines consist of but one track; in Great Britain all possess two tracks, suitable for trains going in opposite directions, besides which there are turn-offs at which quick-going trains may pass those of slower motion. At certain convenient points along the line there are station-houses, at which the trains stop to take up and set down passengers, and there is no stoppage at any other place. On most of the lines there are slow trains, taking goods and second-class, or an inferior kind of carriages, and fast trains, taking only first and second class carriages; some lines also have mail trains, which proceed at more than usual speed, and taking only first-class carriages, stop at fewer places by the way. The first-class carriages are covered, and resemble three coach bodies united, but of more commodious dimensions; second-class carriages are open at the sides, and not lined with any stuffing; a third-class carriages are entirely open; goods carriages are open trucks, on which the articles are piled and fastened; trucks for cattle are open, with a railing round the sides. All the carriages in a train are linked one to the other by strong iron hooks; and to prevent them from shocks against each other, the various carriages are provided with projecting rods on springs, cushioned at the outer extremities. Generally, the fares charged for transmission are higher than they need be; a common charge is at the rate of 3d. per mile for each passenger in a first-class carriage; and it is understood that lower rates would create more than a compensatory amount of traffic. There are certain excellences in the arrangements of all the railways which deserve to be mentioned. Each line, being the property of a private association, is secluded from one end to the other from the intrusion of the public; and therefore no jostling or confusion takes place, either upon entering or leaving the carriages. The rails of one line, likewise, join those of another, by which means carriages generally proceed onwards without changing passengers or luggage. A carriage in which passengers take their seats at London goes straight on to Preston-that is, along the lines of three companies. The extraordinary magnitude of the railway undertakings has enabled the directors to organise rules which could never be enforced in the irregular scramble of stage-coaching. It is customary to dress the subordinate functionaries on all the lines in a uniform resembling that of the London policecach man having his number inscribed in figures on some part of his dress; so that, if any one be guilty of incivility or inattention, he can be easily reported to his superiors. There is one pleasing peculiarity in the arrangements, which is entitled to the highest commendation: it is the rule that no officer shall on any account take a fee from passengers, on pain of instant dismissal. Those who imagine that fees to guards, coachmen, or waiters, are requisite to ensure civility, will be surprised to find that railway attendants are infinitely more polite and attentive than their brethren of the coach conveyances. This, in itself, gives travelling by railway a great superiority over all other modes of public conveyance. The London and Birmingham line, which was the first completed after that of Manchester and Liverpool, has always appeared to us to be among the best managed of the various railways, as well as the most complete in all its arrangements. There are accommodations on this line which are to be seen on no other. On all the lines there are waiting-rooms both for ladies and gentlemen at the different stations; but exclusively of those on this line, there is a large and commodious house of entertainment at the Birmingham terminus, where meals stand ready prepared for the passengers. At Wolverton, a place half way from the metropolis, and where the train stops ten minutes, there is likewise a large establishment in the form of an open booth or shop, where tea, coffee, or viands of a more substantial kind, with different liquors, are sold on the instant to those who require refreshment. Passengers who make the journey for the first time by the mail train, will be amused by observing a travelling post-office in the string of carriages. This "Grand Northern Railway Post-Office," as the inscription on its side denotes, is a carriage consisting of two small apartments, one of which is appropriated to the guard, whose duty is to exchange the bags, and the other is fitted up with a table for sorting letters, and holes round the walls for their reception. The manner in which the duties of the clerk and guard are performed in this flying post-office, is strikingly significant of the new order of things introduced by the railway system. Outside the vehicle a species of net is extended by a hoop, and into this the letter-bags are dropped as the train sweeps onward in its course, the bags which are to be left being at the same time tossed from the window by the guard. The fresh bag of letters being received, it is speedily opened, its contents re-arranged, and a new bag for next town being made up, it is projected as before at the place of its destination. By this means a letter may be written, sent through the postoffice, and delivered at the distance of twenty miles, in the space of a single hour. The number of railway companies incorporated by act of parliament up till January 1839, in Great Britain and Ireland, was 107, and the capital which they Entrance to the Railway Tunnel, Liverpool. London and Birmingham Railway, about one hundred and twelve miles long, connecting the metropolis with the centre of England; the Grand Junction Railway, continuing the London and Birmingham line to that of Liverpool and Manchester, and also to a railway proceeding northward to Lancaster, and thus forming a most important thoroughfare obliquely across the country; the Midland Counties, North Midland, and Great North of England railways, connecting the great seats of trade in Northumberland, Durham, Yorkshire, and Derbyshire, with the London and Birmingham line; the Newcastle and Carlisle Railway, connecting these towns; the Great Western Railway, about one hundred and seventeen miles long, connecting London with Bristol, and with smaller tributary lines opening up the west of England; the South-Western Railway, about seventy-seven miles long, connecting London with Southampton; the Manchester and Leeds Railway, connecting these populous towns. In Scotland, the Edinburgh and Glasgow Railway, and the Glasgow and Ayr Railway, are the principal lines. The greatest of the whole of these undertakings is the Grand Western. This line has two tracks, each of seven feet wide, while on all other railways in this country the width is between four and five feet; the carriages, therefore, which run on the Grand Western, must be necessarily confined to itself. The most prosperous of all the lines is that of the London and Birmingham, the weekly revenue of which is upwards of £16,000: the weekly revenue of the Grand Junction, which joins it, is £9000. The speed at which railway trains usually proceed is from twenty to twenty-five miles per hour, though sometimes it is much more. At the ordinary rate of speed, a journey from London to Liverpool by the mail train is performed in about nine hours; and when railways are extended north to Edinburgh, the journey from London to that city will be performed in eighteen hours, or perhaps less. Travelling by railway at any of the common rates of speed is attended with less personal danger than stage-coaching, because the locomotives are perfectly under control. Any deaths or personal injuries which have occurred on railways, are, with scarcely an exception, attributable to the carelessness of the engine-drivers, and by the employment of a superior class of men to direct the motions of the traius, this fruitful cause of mischief is in the course of being obviated. With this improvement, conveyance by railways will be ranked among the most useful and stupendous inventions of art. Printed and published by W. and R. CHAMBERS, Edinburgh. Sold also by W. S. Orr and Co., London. CHAMBERS'S INFORMATION FOR THE PEOPLE. CONDUCTED BY WILLIAM AND ROBERT CHAMBERS, EDITORS OF CHAMBERS'S ZOOLOGY. PRICE 1d. internal cavity, the stomach, into which the food is received, and where it undergoes a preparation; and the absorption of it into the system takes place by vessels distributed on the walls of this cavity. Plants require nothing but a regular supply of water, with carbonic acid, ammonia, and a small quantity of saline matter dissolved in it; and the conditions of their growth generally afford them a constant supply of these, which they can imbibe by means of their roots and leaves, without moving from the place in which they are once fixed. But animals can only be supported by materials previously organised, all their food being derived from vegetable or animal substances; this is nearly always in a solid state, and has to be reduced to a fluid form in order to be imbibed into the tissues. The life of every animal presents a number of facts for observation; and these may be separated from each other according to their character. Thus, we might consider their structure only-the department of science which is termed anatomy. Or we might examine their actions or functions-in fact, the history of their lives THE branch of Natural History termed ZOOLOGY, is these, however, we might restrict our inquiries to a -which is termed physiology. In pursuing either of that which treats of the beings composing the Animal single animal, though it would not be advantageous to Kingdom. The general aspect of these, and the cha- do so. racters by which they may be ordinarily distinguished sees that the several beings included in the Animal The objects of the zoologist are different. He from plants, are under the observation of every one, Kingdom may be regarded not only in their individual and they need not here, therefore, be dwelt upon. is only when we descend the scale, and arrive at the form parts of one vast plan, as harmonious in itself as It aspect, but in their relations to each other; that they lowest and simplest of each kingdom, that the characters that of a beautiful building made up of a vast number upon which we have been accustomed to rely succes- of subordinate parts; and that, whilst the diversities of sively disappear, and we meet with several tribes which form and aspect seem almost infinite, they are evidently it is very difficult to assign with certainty to either subordinate to certain general principles, which pronatural division. Thus, there are many animalcules in duce not only the manifest conformity, but the apparent which no structure characteristic of the Animal King- departures from it. The grand aim of the scientific dom can be discovered; and yet they exhibit an acti- zoologist being to discover this plan, he employs classivity of motion, evidently influenced by the sensations fication as a means by which to facilitate his acquaintthey experience, which shows them to be far removed ance with the vast number of beings that claim his from plants. It is when the characteristic structure of attention. animals, and the manifestations of sensibility and power of spontaneous movement, disappear together, as is the case in the sponge, that the naturalist is the most perplexed in regard to the place he shall assign to such beings; and he can only solve the question, by ascertaining whether the general resemblance is the greatest to beings of distinctly animal or of distinctly vegetable character. By this criterion, the sponge will hereafter be found to deserve a place in the Animal Kingdom. The differences of structure which are most universally found to separate animals from plants, are those which are connected with the mode in which food is assimilated (or converted into the materials of their own fabric) by the beings of the two kingdoms respectively. Thus, it may be constantly noticed that plants imbibe their nourishment either through their external surface or by prolongations of this into roots and leaves. On the other hand, animals nearly always possess an 449 CLASSIFICATION. such as we are familiar with as inhabitants of this On looking at the variety of animal forms around us country, or as natives of other climates collected for our observation-the mind naturally associates together those which have the greatest general resemblance, and separates these (although differing in some degree greater dissimilarity. It is by pursuing this plan, from amongst themselves) from those with which they have one stage or degree of resemblance and difference to another, that classifications are formed; and these will be correct according to the amount of knowledge upon which they are founded, respecting not only the external form but the internal structure of the objects they include. of animal is similar to its parents, though slight variaExperience teaches that the offspring of any kind tions may be often traced between them; but a suc- | differently formed in the different classes, they are cession of beings having this general conformity is essentially the same in all. The arms and legs of man, called a race. Now, the first object which the natu- the four legs of a quadruped, the wings and legs of a ralist has to determine is, whether two races, such bird, and the fins of a fish, are all exactly alike in their as the Negro and European races of man, or any two position, and in the elements of which they are combreeds of dogs, might have had a common origin. If posed. The skeleton of the Vertebrata is internal, he finds reason to believe that their differences are being clothed with the muscles by which its various not greater than may be accounted for by the influ- parts are moved; and, from what has been said, it is ence of accidental causes, and especially if he finds evident that it is particularly destined for the protecone race ever producing the form of another, he con- tion of the nervous system, which, from the high place siders them as springing originally from a common of this group in the scale of animal beings, is the organ stock, and as of one species; but if he cannot thus ac- of the greatest importance in the whole structure. count for their differences, he regards them as of dif- Vertebrated animals are endowed with all the special ferent species. This division of all the existing forms senses-sight, smell, hearing, and taste the organs of of animals into species is that on which the naturalist which are situated in the head; besides the general has to found all his subsequent classification; and it is sense of touch, which is common to the whole body. necessary to take great care to avoid errors arising They have all red blood, which is propelled through from variations in the forms of animals at different the system by a muscular heart. The mouth is furperiods of their existence. nished with two jaws, which are placed one above or before the other; there are never more than two, and they never open sideways as in the Articulata. They are usually armed with teeth, which are in structure very analogous to bone. A number of species, differing from each other in trivial points, but having a strong general resemblance, are said to belong to one genus. The genera most nearly allied are united into one family; several families into an order; and several orders into a class. The class, therefore, contains a very large number of species, many of them differing widely from each other, but all agreeing in some prominent and important character. And the classes composing the Animal Kingdom are arranged under four groups, on account of their correspondence in certain general particulars, and their difference in others: these are called sub-kingdoms. This is the alphabet of the science; and when this has been acquired, the student will proceed to his grammar, which consists of such a knowledge of the principal divisions of the animal kingdom, as will enable him to read the language of nature with understanding, so as to learn from the simple name much respecting the structure and character of the particular specimen, of which he would otherwise be ignorant. PRIMARY DIVISIONS OF THE ANIMAL KINGDOM. The Vetebrata are characterised by a higher degree of intelligence than is possessed by any other group. The animal powers of sensibility and spontaneous motion are also greatly developed; and in accordance with these, a complete symmetry or correspondence between the two sides of the body is observable externally. But this symmetry does not extend to the organs of vegetative life, which are irregularly disposed in the cavities which they occupy. In the ARTICULATA, the skeleton is external, enveloping not only the nervous system but the entire body, with the muscles which move it; these, as is well seen in the crab or lobster (which are the largest animals of this group), being attached to the interior of the firm casing. This skeleton is formed of a number of pieces or segments, jointed or articulated togetherwhence the name of the group. The centipede is a very characteristic illustration of this structure. The legs, as well as the body, are here seen to be enclosed in a firm envelope, of which the pieces are connected together by a flexible membrane; and the segments of the body are nearly alike along its entire length. But in the higher classes of this sub-kingdom, where the movement is performed entirely by the legs, as in Crustacea, or by the legs and wings, as in Insects, the segments of the body to which these are attached are firmly united together, in order to give their muscles a fixed In considering the primary subdivisions of the Animal Kingdom, it is desirable to view them at first in their most simple aspect, and to regard merely the points of agreement amongst all the beings contained in each group, and their most striking differences from the members of other groups. The subordinate differences amongst the forms contained in any one of the primary groups, will be subsequently attended to. Following the arrangement of Cuvier, which in this respect is unexceptionable, we divide the animal king-point from which to act. But, in the lower classes, such dom into four sub-kingdoms-VERTEBRATA, ARTICULATA, MOLLUSCA, and RADIATA. The principal characteristics of these will now be pointed out. The VERTEBRATA derive their name from the peculiarity of their skeleton, which essentially consists of a back-bone or spinal column, formed of a number of separate pieces, so united as to combine great strength with flexibility. These are termed vertebra. Each is perforated with a large aperture; and, when all are united, a continuous tube is formed, in which is lodged the spinal marrow, a very important part of the nervous system (this is quite different from the marrow of other bones, which is an oily substance, subservient to their nutrition). At one extremity, the spinal column is extended into a large bony structure, the skull, which is especially designed for the protection of the brain (a large nervous mass, which may be regarded as an expansion of the spinal marrow) and of the organs of sense connected with it. At the other extremity it is contracted into a tail, the size and prolongation of which are usually greater in proportion to the small size of the skull. Connected with this spinal column are a series of ribs, which pass off from it on each side, and generally meet again in a breast-bone, enclosing a cavity (that of the chest), in which are contained some of the organs of nutrition. Appended to it are two pairs of members or extremities, which are usually the instruments of locomotion. Although these are very as the leech and worm, where the extreme flexibility of the body, and the change of its dimension, are the only means of locomotion (no members being present), the whole envelope of the body is so soft, that the division into segments is scarcely perceptible. The nervous system of the Articulata is not by any means so highly developed as that of the Vertebrata; in general, the organs of taste and vision are all that can be detected in them; those of hearing and smell being possessed only by a few of the higher tribes. The number of legs, when these are present, is often very great; they are never less than six. More than one pair of jaws usually exist, and they open laterally. The blood is white, and only in the highest classes is propelled by a powerful heart. The Articulata have their whole structure adapted to great activity of locomotion, and to the performance of instinctive actions of a high character. The class in which this is most evident—that of Insects is by far the largest in the whole animal kingdom. The body, which is usually of small size, derives its principal bulk from the orgaus of animal life, especially the muscles which move the extremities; and the lateral symmetry is even more remarkable in them than in the Vertebrata, extending in part to the organs of nutrition as well as to those of sense and motion. The group of MOLLUSCA must be described more by its negative than its positive characters. The body, as the name imports, is here soft, and destitute of any dis |